Filament joint for electric lamps or similar devices



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June 6, 1961 s, c, ACKERMAN 2,987,643

FILAMENT JOINT FOR ELECTRIC LAMPS OR SIMILAR DEVICES Filed May 2, 1956United States Patent York Filed May 2, 1956, Ser. No. 582,290 Claims.(Cl. 313271) My invention relates in general to electric incandescentlamps and similar devices and more particularly to an improved joint orconnection between the filament and leading-in conductors of suchdevices.

In the service for which certain types of incandescent lamps areintended, the lamp is normally subjected to constant or prolongedperiods of severe vibration. This is particularly true, for instance, inthe case of lamps employed for aircraft service such as aircraft landinglamps. Where the filaments of such lamps, as in the case of theaforementioned aircraft landing lamps, are unsupported except for theirpoints of connection to the lead-in conductors or wires of the lamp, theresulting flexure of the filament produced by the vibration of the lampsubjects the filament connections or joints to severe stresses. Adequatefilament or mount strength against such vibration and resulting stressestherefore becomes an important factor in the construction of such typelamps.

In the manufacture of incandescent lamps designed for such severevibration service, as for example in the manufacture of aircraft landinglamps, it has been common practice to connect the filaments to thelead-in conductors of the lamp by welding the end legs of the filamentto the lead-in conductors. These filaments are conventionally formed oftungsten wire. However, when a refractory type metal like tungsten iswelded to the lamp lead-in conductors, a re-crystallized area with verycoarse grain structure is very apt to develop in the filament wire atthe region of the welded joint or connection, even though the mostcareful control is exercised over the welding operation. With theformation of this large crystal growth in the tungsten filament wire,the tungsten becomes brittle at the welded joint or connection. Theresult is a filament joint or connection of relatively low strength andinadequate resistance to Withstand the stresses such as are imposed onthe joint by the vibration normally encountered in aircraft service.

It is an object of my invention, therefore, to provide an electricincandescent lamp or similar device with a filament joint of improvedstrength and resistance to vibrational stresses. Another object of myinvention is to provide an electric incandescent lamp or similar devicehaving a welded type filament joint of a construction such that thepoints of maximum stress developed in the filament on vibration arelocated at regions inwardly of the filament from the regions of theirwelded connections to the support or lamp lead-in members.

Briefly stated, in accordance with one aspect of my invention, the endlegs of the filament are mechanically connected or clamped to thelead-in conductors of the lamp by thin metal strap or plate memberssuitably secured to the lead-in conductors as by welding, and thefilament end legs are welded to the said metal strap members at pointsoutwardly of the filament relative to their points of mechanicalattachment to the lead-in conductors by the strap members.

Further objects and advantages of my invention will appear from thefollowing detailed description of a species thereof and from theaccompanying drawing.

In the drawing, FIG. 1 is an elevation, in section, of

an electric incandescent lamp comprising my invention.

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FIG. 2 is a perspective view, on an enlarged scale, of the mountstructure of the lamp shown in FIG. 1.

FIG. 3 is an elevation, partly in section and on an enlarged scale, ofthe filament joint comprising my invention, and

FIG. 4 is a transverse section, on a greatly enlarged scale, of themount structure and showing one of the filament joints thereof insection.

Referring to the drawing, the lamp there illustrated is of theself-contained reflector type described and claimed in U.S. Patent2,148,314, D. K. Wright, issued February 21, 1939, and assigned to theassignee of the present invention. The lamp comprises a bulb or envelope1 consisting of a preformed pressed glass reflector section 2 sealedaround its periphery to a preformed pressed glass cover section 3. Theinterior surface of the reflector section 2 is of suitablelight-concentrating shape such as paraboloidal, for instance, and it iscovered with a metallic coating 4, preferably of aluminum, constitutinga re fleeting surface. Mounted on the reflector section 2, exteriorlythereof and at the apex of said section, is a base structure 5. The basestructure 5 may be of the type described and claimed in U.S. Patent2,272,512, Cotman et al., dated February 10, 1942, and comprising a pairof metal lugs 6 suitably secured, as by soldering, to metallic cups orthimbles 7 having their edges sunk and embedded in the glass of thereflector section 2 around openings 8 therein, the cups or thimbles 7thus hermetically closing the said openings 8. The envelope 1 isexhausted and filled with a suitable gas through an exhaust tube 9attached to the reflector section 2 at its apex. After the gas fillingis introduced into the lamp envelope, the exhaust tube 9 is tipped off,as indicated at 10, to hermetically seal the envelope.

Mounted within the envelope 1 and supported therein from the metalthimbles 7 is a mount structure 11 comprising an electric energytranslation element or filament 12 disposed between and connected to apair of rigid lead- -in wires or conductors 13 of suitable material,such as nickel or iron. The lead-in conductors 13 are rigidly secured attheir outer ends to the metal thimbles 7, as by soldering or brazing,and they extend straight through the openings 8 in the reflector sectioninto the interior thereof in parallel relation to one another andpreferably in a plane parallel to and including the axis of thereflector section 2. The lead-in conductors 13 are held in rigid spacedrelation by an insulating bridge or cross bar member comprising a glassrod 14 extending between and secured to the lead-in conductors 13 byshort fastening wires 15 which may be spot-welded to the lead-inconductors. The inner end of one of the lead-in conductors 13 is formedwith a lateral extension 16 to which is secured a shield 17 forintercepting certain of the direct radiations from the filament whichotherwise would pass out through the cover glass 3 of the lamp envelope.

The filament 12 comprises a linear coiled-coil (the filament proper) oftungsten wire disposed coaxially of the reflector axis in a position indefinite optical relation to the focus of the reflecting surface 4,preferably symmetrically about the reflector focus. Each end of thefilament 12 is provided with a straight or uncoiled end section or legportion 18 extending laterally of the lead-in conductors 13 and overwhich is slipped a coil 19 of a suitable heat-resisting metal such astungsten or molybdenum or an alloy thereof. The slip-over coil 19 iswound with a relatively close pitch, i.e. closely coiled, and ispreferably made just large enough in diameter to fit more or less snuglyaround the filament end leg 18.

The coil-enclosed end legs 18 of the filament 12 are connected to therespective lead-in conductors 13 by a filament joint or connection 20constructed in accordance with the invention. To this end, eachcoil-enclosed file 3 l ment end leg 18 extends across and is firmlypressed or clamped against the respective lead-in conductor 13 by a thinmetal strap or plate member 21 which is securely fastened to the lead-inconductor in any suitable manner, for instance, as by welding it to thelead-in conductor at points on either side of the filament end leg 18,as indie cated at 22. The tight clamping of the coil-enclosed filamentend leg 18 to the lead-in conductor 13 thus forms a rigid mechanicalclamp connection therebetween which constitutes the first point ofcompletely rigid anchorage of the filament end leg outwardly therealongfrom the main body of the filament or filament proper. The metal strapor plate members 21 may be made of any suitable material such as nickelor iron for example, and they are fastened to the lead-in conductors ina manner such as to extend outwardly away from the said conductors inopposite directions therefrom and substantially in the plane of the saidconductors 13 whereby the plate members 21 intercept a minimum of theradiations from the filament so as not to produce undesirable shadows ordark spots in the light beam projected by the lamp.

In accordance with the invention, each filament end leg 13, instead ofbeing welded directly to the lead-in conductor 13 as in priorconstructions, is extended outwardly beyond the lead-in conductor and iswelded to the metal strap or plate member 21 at a point along its lengthspaced some distance, for example, one-eighth inch or so outwardlythereof from its mechanical clamp connection to the lead-in conductor asindicated at 23. In the particular case illustrated, the metal strap orplate members 21 are formed of sheet metal having a thickness preferablyof about .020 inch for example, and they are of rectangular shape havinga length along the leadin conductors of around one-half inch tofive-eighths inch and a width or" the order of one-quarter inch. Asshown in FIG. 1, the strap or plate members 21 are each formed with across corrugation 24 extending thereacross and preferably tapered downin size (i.e. both in width and depth) in a direction outwardly from therespective leadin conductor to provide a correspondingly tapered grooveor channel 25 for accommodating the coil-enclosed filament end leg 18therein. This tapering of the channel or groove 25 in the metal strap 21serves to raise or expose the coil-enclosed end leg 18 of the filamentabove the plane of the Welding faces of the metal strap, therebyassuring contacting of the welding electrode with the coilenclosedfilament end leg during the welding thereof to the metal strap 21.

By shifting the welded connection 23 between the coilenclosed filamentend leg 18 and the lead-in member 13, 21 to a point outwardly of thelead-in conductor 13 relative to the filament in accordance with theprinciple of my invention, so that the first point of completely rigidanchorage of the filament end leg outwardly therealong from the filamentproper is its mechanical clamp connection to the lead-in conductor 13 bythe clamping strap or plate member 21, the points of maximum fiexurestress that develop in the filament on vibration thereof then occur atthe mechanical pressure or clamp connection of the coil-enclosedfilament end leg to the lead-in conductor and are thus kept away fromthe re-crystallized section of the filament which is produced at theweld 23 thereof to the metal strap 21. As a result, a filament joint 20is provided of greatly increased vibration strength over that which isobtained where the filament is welded directly to the lead-in conductorso that the points of maximum fiexure stress in the filament are locatedat the welded and re-crystallized section of the filament. The outwardshifting of the welded connection between the filament end leg and thelead-in conductor in the manner disclosed also provides an added safetyfactor in that the filament end leg 18 is secured at two differentpoints to the lead-in member 13, 21. The metal strap or plate members21, in addition to serving as a means of locating the welded connectionof the filament to the lead-in 4 l conductor at a point outwardly of theconductor relative to the filament, also serve as a means fordissipating the heat from the filament joint 20 so as to maintain thefilament joint at a minimum operating temperature below that temperatureat which distortion. of the lead-in conductors might occur. Moreover,because of the increased current-carrying cross section whichtheyprovide at the filament joints, the metal straps or plate members 21further serve to diminish the rate of heating of the filament joints bythe current passing therethrough during lamp operation.

Although a preferred embodiment of my invention has been disclosed, itwill be understood that the invention is not to be limited to thespecific construction and arrangement of parts shown, but that they maybe widely modified within the spirit and scope of my invention asdefined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an electric lamp, the combination of a lead-in conductor, afilament having an end portion extending across and beyond saidconductor, and a metal plate member secured to said conductor over andtightly clamping said filament end portion to said conductor to form arigid mechanical clamp connection therebetween, said mechanical clampconnection constituting the first point of completely rigid anchorage ofthe said filament. end portion outwardly therealong from the filamentproper, said filament end portion being welded to said metal platemember at a point along the length of said filament end portionoutwardly thereof from its said mechanical clamp connection to'saidconductor and being entirely free of welded regions inwardly of its saidpoint of welded connection to the metal plate member,

2. In an electric lamp, the combination of a lead-in conductor, afilament having an end portion extending across and beyond saidconductor, and a metal plate member welded to said conductor on eachside of and extending over the said filament end portion and tightlyclamping it to said conductor to form a rigid mechanical clampconnection therebetween, said mechanical clamp connection constitutingthe first point of completely rigid anchorage of the said filament endportion outwardly therealong from the filament proper, said filament endportion being welded to said metal plate member at a point along thelength of said filament end portion outwardly thereof from its saidmechanical clamp connection to said conductor and being entirely free ofwelded regions inwardly of its said point of welded connection to themetal plate member.

3. In an electric lamp, the combination of a lead-in conductor, afilament having an end portion extending across and beyond saidconductor, a slip-over coil on the said end portion of the saidfilament, and a metal plate member secured to said conductor over andtightly clamping the said coil-enclosed filament end portion to saidconductor to form a rigid mechanical clamp connection therebetween, saidmechanical clamp connection constituting the first point of completelyrigid anchorage of the said coil-enclosed filament end portion outwardlytherealong from the filament proper, said coil-enclosed filament endportion being welded to said metal plate member at a point along thelength of said filament end portion outwardly thereof from its saidmechanical clamp connection to said conductor and being entirely free ofwelded regions inwardly of its said point of welded connection to themetal plate member.

4. In an electric lamp, the combination of a lead-in conductor, afilament having an end portion extending across and beyond saidconductor, a slip-over coil on the .said end portion of the filament,and a metal plate member extending over and tightly clamping saidcoil-enclosed filament end portion against said lead-in conductor to.form a rigid mechanical clamp connection therebetween, said mechanicalclamp connection constituting the first point of completely rigidanchorage of the said filament end portion outwardly therealong from thefilament proper, said metal plate member being welded to the lead-inconductor at points on opposite sides of the coil-enclosed filament endportion and said coil-enclosed filament end portion being welded to saidmetal plate member at a point along the length of said filament endportion outwardly thereof from its said mechanical clamp connection tosaid conductor, said coil-enclosed filament end portion being entirelyfree of welded regions inwardly of its said point of welded connectionto the metal plate member.

5. In an electric lamp, the combination of a lead-in conductor, afilament having an end portion extending across and beyond saidconductor, a slip-over coil on the said end portion of the filament, anda metal plate member secured to and extending alongside said lead-inconductor and over said coil-enclosed filament end portion and tightlyclamping it against said lead-in conductor to form a rigid mechanicalclamp connection therebetween, said mechanical clamp connectionconstituting the first point of completely rigid anchorage of the saidfilament end portion outwardly therealong from the filament proper, saidmetal plate member having a groove therein within which the saidcoil-enclosed filament end portion fits, said groove slightly taperingdown in size in a direction outwardly of the plate member from theifilament so as to accommodate within its smaller size end region less thanthe full diametrical width of the coil-enclosed filament end portion,said filament end portionbeing welded to said metal plate member at apoint along the length of said filament end portion outwardly thereoffrom its said mechanical clamp connection to said conductor and beingentirely free of welded regions inwardly of its said point of weldedconnection to the metal plate member.

References Cited in the file of this patent UNITED STATES PATENTS1,829,423 Sutherlin Oct. 27, 1931 2,247,688 Kinyon July 1, 19412,366,292 Smith Jan. 2, 1945 2,404,992 Stone July 30, 1946 2,632,126Curtis Mar, 17, 1953 2,716,714 Adams Aug. 30, 1955 2,738,435 VoreauxMar. 13, 1956 2,791,713 Dean May 7, 1957 2,791,714 Beesley May 7, 1957

